This invention relates generally to the field of electrical stimulators, and more particularly to cardioverters and defibrillators.
The earliest cardioverters and defibrillators generated either a single burst of alternating current or a single pulse for application to the heart to cause cardioversion or defibrillation. However, the use of multiple pulses to accomplish cardioversion or defibrillation has also been extensively researched. For example, U.S. Pat. No. 3,605,754 issued to Jaros, et al., on Sep. 20, 1971 discloses an early double pulse heart defibrillator employing two capacitors which are successively discharged between a single pair of electrodes. Later, the use of multiple electrode systems, in which defibrillation pulses were delivered successively between different electrode pairs chosen from among the electrodes available was suggested. For example, U.S. Pat. No. 4,727,877 issued to Kallok on Mar. 1, 1988 and U.S. Pat. No. 4,708,145 issued to Tacker, Jr. et al., on Nov. 24, 1987, both disclose a variety of implantable, multiple electrode systems adapted for use in conjunction with a sequential pulse defibrillator, in which pulses are applied sequentially to different pairs of electrodes.
More recently, delivery of pulses simultaneously between multiple electrode pairs has been extensively pursued. For example, U.S. Pat. No. 4,953,551, issued to Mehra et al., on Sep. 4, 1990, discloses simultaneous delivery of pulses between the superior vena cava and the right ventricle and between the right ventricle and a subcutaneous electrode.
The ability to deliver sequential and simultaneous pulses to different pairs of electrodes is incorporated in the Mealtronic implantable pacemaker/cardioverter/defibrillators presently in commercial distribution in the United States. Pulse generation circuitry for delivering such pulses is disclosed in U.S. Pat. No. 5,163,427 issued to Keimel. In the Keimel patent, two capacitor banks are provided which are simultaneously charged and then successively or simultaneously discharged between different pairs of electrodes.
It has also been proposed to apply biphasic pulses to individual electrode pairs, in which a positive pulse is followed by a negative pulse, typically having an initial amplitude equal to the trailing edge amplitude of the first pulse, but at a reversed polarity. Apparatus for delivering such biphasic pulses are disclosed in U.S. Pat. No. 4,850,357 issued to Bach, Jr. on Jul. 25, 1989, U.S. Pat. No. 4,953,551 issued to Mehra et al., on Sep. 4, 1990, and in U.S. Pat. No. 4,800,883 issued Jan. 31, 1989 to Winstrom. In all three references, it is proposed to deliver the biphasic pulse by the use of a single capacitor or a capacitor bank in which capacitors are charged and discharged together to deliver the biphasic pulse.
An alternative multiple pulse, multiple electrode defibrillation pulse regimen, referred to as the "peripheral rotating pulse" regimen, is disclosed in U.S. Pat. No. 4,641,656, issued to Stairs. This patent proposes delivery of sequential pulses, each of which employs a set of three or more electrodes, with the relative polarities of one or more electrode pairs reversed between pulses, This pulse regimen provides the ability to alter the defibrillation pulse vector between pulses, without leaving one or more electrodes inactive during individual pulses. In addition, at those electrodes which have their polarities reversed, a biphasic waveform is effectively provided.